Downlink and uplink array and beamforming arrangement for wireless communication networks

ABSTRACT

System and methods of cellular communications network are described herein. In one system, an antenna array is described. The antenna array has a first beamforming arrangement for producing uplink beams and a second beamforming arrangement for producing downlink beams. The first and second beamforming arrangements are different from one another. The wireless communication network communicates with a mobile station by use of the uplink and downlink beamforming arrangements.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.12/857,622 entitled “DOWNLINK AND UPLINK ARRAY AND BEAMFORMINGARRANGEMENT FOR WIRELESS COMMUNICATION NETWORKS” to Smith et al., filedAug. 17, 2010, which is a continuation of U.S. patent application Ser.No. 10/358,914 entitled “DOWNLINK AND UPLINK ARRAY AND BEAMFORMINGARRANGEMENT FOR WIRELESS COMMUNICATION NETWORKS” to Smith et al., filedFeb. 5, 2003, now U.S. Pat. No. 7,792,547, all of which are incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to an antenna array and beamforming arrangementfor a base station in a wireless communications network. It isparticularly applicable, but in no way limited, for use in a cellularcommunications network, for transmitting and receiving signals to andfrom mobile stations such as mobile phones or personal data assistants.

BACKGROUND

The term “wireless communications network” is used herein to refer to acommunications network comprising at least one base station transceiverarranged to communicate with at least one mobile station. It will beappreciated by those skilled in the art that a wireless communicationsnetwork will often take the form of a cellular communications network,in which a plurality of base station transceivers each define ageographical cell. Mobile stations located in the communications networkcommunicate with one or more base station transceivers, for example, theclosest one to the mobile station. Each base station transceiver has alimited range and a cell can be considered to be a geographical regionover which a base station transceiver can communicate effectively with amobile station therein.

Mobile stations such as mobile telephones may be located within acellular communications network to send and receive signals to and fromthe base station transceivers. Each mobile station operating within acell requires a certain amount of bandwidth to operate and because thetotal bandwidth of base station transceivers is limited the number ofmobile stations which can operate within a cell is limited.

The provision of base stations is expensive. Firstly, the location andsurveying of suitable sites for base stations is time consuming andcomplex since the location of any one base station impacts the basestation requirements for adjacent cells. Furthermore, obtaining planningor zoning permission for base stations is becoming increasinglydifficult as a result not least of concerns about electromagneticemissions and the aesthetic impact of antenna towers.

Accordingly, there is a general desire to minimise the number of basestations. This may be achieved by improving the coverage of basestations i.e. the geographical area over which sufficient radiatedpowers are produced to allow effective communication with mobilestations and/or increases in capacity i.e. the number of mobile stationswhich may be supported by a single base station. Assuming that theseaims may be met without a disproportionate increase in base stationcosts, it is generally understood that a reduction in the number of basestations is desirable.

One traditional approach to this problem has been to increase“sectorisation” at the base, i.e. to use a single base station locationto provide coverage in different “sectors” which are arranged radiallyaround the base station location.

Many existing systems use “tri-sectoring” in which three sectors arecovered using a single base station. The prior art tri-sectoringarrangement increases both uplink and downlink capacity by a factor ofalmost three compared to a basic omni-directional arrangement. However,the improvement is less than three times since perfect sectorisation isnot possible i.e. there is always some overlap between adjacent sectors.This loss is called partition loss and typically increases with thenumber of sectors at the base. Using multibeam technology to replaceeach sector with an array, allows beams to be formed which are narrowerthan the full sector width. This has a similar effect to increasedsectorisation and thus improves capacity. These arrays may for examplecomprise a plurality of columns of antenna elements which may or may notbe combined using a beam former to produce a lesser or equal number ofbeams by combining the outputs of the columns, for example using aButler matrix. For N columns there can be up to (and including) Northogonal beams.

Typically each such sector uses an antenna having a plurality ofelements which provide a plurality of beams. Typically three fixed beamsare used both for uplink and downlink connections in each sector. Thusin the prior art, an antenna may be used to provide three sectorcoverage with three beams in each of these sectors. Using an array foreach sector, narrower beams may be used which may be directed when theantenna is configured, to different parts of the sector. Since the beamstypically overlap, additional information is available on the uplinkwhich may be used using conventional space-time signal processingtechniques, to provide additional spatial processing gain in the uplink.

These steps have gone some way towards providing increased capacity inbase stations. Nevertheless, it is anticipated that capacityrequirements will increase three or four fold from present day levelswithin a short space of time. This capacity requirement cannot be metwith a three or four fold increase in the number of base station sitesfor at least the reasons explained above. Thus yet further improvementsto base station capacities are required.

U.S. Pat. No. 6,480,524 describes a six column array for the downlinkusing a three way beam former which gives good capacity benefits. Whilstit would be possible to produce three beams from a three column array,the use of a six column array allows more control of the beam shape. Byshaping the beams with “deep cusps” (by using multiple elements for eachbeam) overlap between the beams is reduced which in turn reduces“partition loss”. This partition loss is characterised in part byinterference between adjacent beams directed to different mobilestations within a sector and also by increased hand-off overhead asmobile stations hand-off back and forth between overlapped beams. Thusin the case of the downlink, there are significant advantages inreducing overlap, as explained in U.S. Pat. No. 6,480,524.

In terms of apparatus size, for the downlink it would be possible to usea six column array at the top of the mast, and maximum downlink capacitywould be achieved by forming six beams with this array. However, eachdownlink beam would require an expensive power amplifier, together withcabling up the mast. As mentioned above, using fewer beams than columnsalso provides improved beam shapes. Thus, a good cost/capacity tradeofffor the downlink is a 6 column array with 3 deep cusp beams.

A further consideration in base station design is the possibility ofusing the same antenna array both for the uplink and downlink. The useof separate arrays requires larger areas of land and also generally hasincreased aesthetic impact. Where the arrays are mounted on the samestructure, additional arrays also produce increased wind loadingproblems. Thus it is generally desirable to attempt to use the samearray i.e. a common array, both for the uplink and downlinkcommunications. However, this may place compromises on the design of theuplink antenna which typically is configured (i.e. constructed and fed)identically to that of the downlink.

Thus in practice, the capacity of a state-of-the-art base station isasymmetric i.e. greater downlink capacity is available than uplinkcapacity. Whilst this may be suitable for some data applications such asweb-browsing or streaming video, it is unsuitable for applications suchas voice communications.

SUMMARY

According to a first aspect of the invention there is provided anantenna array suitable for use in a base station in a wirelesscommunications network, the antenna array having a first beamformingarrangement for producing uplink beams and a second beamformingarrangement for producing downlink beams, wherein the first and secondbeamforming arrangements are different from one another. The use of twobeamforming arrangements provides the advantage that the number andshape of beams on the uplink and downlink can be independently designedto suit their differing requirements, resulting from differentcost/capacity tradeoffs.

This array takes advantage of the different technical considerations forthe uplink as compared to the downlink. Thus for example in the sixcolumn array described in U.S. Pat. No. 6,480,524, all six columns maybe used as separate uplink receiver branches. In general, a large numberof separate antenna elements for the uplink is desirable since thisimproves the space combiner gain and this being the case, beam overlapproblems are less significant than in the downlink. Furthermore, thecost implications of multiple antenna elements is different. Poweramplifiers for the downlink are considerably more expensive than lownoise amplifiers required for the uplink and thus as explained in moredetail below, the cost and cabling trade-offs for the uplink aredifferent to those for the downlink. It has been found that theincreased costs of using a separate beam forming arrangement for theuplink are more than outweighed by the improvements in uplink capacityfor the base station.

Preferably the first and second beamforming arrangements feed a commonantenna array to produce the uplink and downlink beams. A common arrayis an array which is used for both transmitting and receiving signals.Using a common antenna array provides the advantage that separateantenna arrays for the uplink and downlink are not required.

Preferably a plurality of (sin x/x) beams are formed for the uplink, anda plurality of low cusp beams are formed for the downlink. Preferablythese beams are dual polar, and thus the antenna may advantageously bearranged to achieve diversity gain from the dual polar beams in both thedownlink (transmit diversity) and uplink (receive diversity) directions.

In a preferred embodiment, the antenna array is arranged such that threedual polar low cusp beams are formed for the downlink, and six dualpolar (sin x/x) beams are formed for the uplink.

The antenna array may have a six column arrangement in which the sixantenna column outputs are fed directly to the receiver equipment forcombination, rather than being combined at the masthead in a beamformerto give beams.

The number of uplink beams produced by the first beamforming arrangementmay be twice as many as the number of downlink beams produced by thesecond beamforming arrangement. This enables the uplink capacity to beenhanced by a factor of approximately 2 times, without impacting thedownlink performance, whilst still using a common array.

In one preferred embodiment, the number of uplink beams is four and thenumber of downlink beams is two. In another preferred embodiment, thenumber of uplink beams is six and the number of downlink beams is three.

The second beamforming arrangement may be configured to transmitmultiple input multiple output (MIMO) transmissions. The firstbeamforming arrangement may also in principle be configured to receiveMIMO transmissions.

Preferably the antenna array comprises a three beam downlink, a six beamuplink, and a plurality of circulators. Alternatively the antenna arraymay comprise a three beam downlink, a six beam uplink, and a pluralityof filters to separate the uplink and downlink signals, the filtersbeing arranged to discriminate on the basis of frequency. A secondalternative for time domain duplexed systems (as currently deployed forWireless LAN or UMTS in time domain duplex mode) would use multipleswitches to separate the uplink and downlink signals

The uplink arrangement may use maximal ratio combining or minimum meansquared error combining.

A separate pilot may be used on each of the downlink beams. On theuplink, individual pilot signals are typically transmitted by eachmobile station.

According to a second aspect of the invention there is provided amasthead of a base station transceiver including an antenna array havinga first beamforming arrangement for producing uplink beams and a secondbeamforming arrangement for producing downlink beams, wherein the firstand second beamforming arrangements are different from one another.

According to a third aspect of the invention there is provided acellular communications network including an antenna array having afirst beamforming arrangement for producing uplink beams and a secondbeamforming arrangement for producing downlink beams, wherein the firstand second beamforming arrangements are different from one another.

According to a fourth aspect of the invention there is provided acellular communications network comprising a plurality of cells, whereina plurality of said cells each contains a base station transceiverhaving a first beamforming arrangement for producing uplink beams and asecond beamforming arrangement for producing downlink beams, wherein thefirst and second beamforming arrangements are different from oneanother.

For each base station transceiver, preferably the first and secondbeamforming arrangements feed a common antenna array to produce theuplink and downlink beams.

Preferably a plurality of (sin x/x) beams are formed for the uplink, anda plurality of low cusp beams are formed for the downlink. Preferablythese beams are dual polar.

Particularly preferably each antenna array is arranged such that threedual polar low cusp beams are formed for the downlink, and six dualpolar (sin x/x) beams are formed for the uplink.

According to a fifth aspect of the invention there is provided a basestation transceiver for use in a wireless communications network, thebase station transceiver having an antenna array, the antenna arrayhaving a first beamforming arrangement for producing uplink beams and asecond beamforming arrangement for producing downlink beams, wherein thefirst and second beamforming arrangements are different from oneanother.

Preferably the first and second beamforming arrangements feed a commonantenna array to produce the uplink and downlink beams.

Preferably a plurality of (sin x/x) beams are formed for the uplink, anda plurality of low cusp beams are formed for the downlink. Preferablythese beams are dual polar.

Particularly preferably the antenna array is arranged such that threedual polar low cusp beams are formed for the downlink, and six dualpolar (sin x/x) beams are formed for the uplink.

According to a sixth aspect of the invention there is provided a radiosignal received on a plurality of (sin x/x) beams forming an uplink of acellular communications network.

According to a seventh aspect of the invention there is provided anantenna array suitable for use in a base station in a wirelesscommunications network, the antenna array having a plurality of antennaelements of which at least some are combined to form a beam fortransmitting downlink signals and at least some are used to form a beamfor receiving uplink signals, wherein the uplink and downlinkbeamforming arrangements are different from one another.

According to an eighth aspect of the invention there is provided amethod of operating a wireless communications network, comprising usingan antenna array having a first beamforming arrangement to produceuplink beams and a second beamforming arrangement to produce downlinkbeams, wherein the first and second beamforming arrangements aredifferent from one another.

Preferably the method further comprises using a common antenna array toproduce the uplink and downlink beams.

Preferably the method further comprises forming a plurality of (sin x/x)beams for the uplink, and a plurality of low cusp beams for thedownlink.

In a preferred embodiment the method further comprises forming threedual polar low cusp beams for the downlink, and six dual polar (sin x/x)beams for the uplink.

Preferably the method comprises combining at least some of the antennaelements to form a beam for transmitting downlink signals and using atleast some of the antenna elements to form a beam for receiving uplinksignals, wherein the uplink and downlink beamforming arrangements aredifferent from one another.

Preferably the wireless communications network is a cellular wirelesscommunications network.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates uplink array processing options, associatedimplementation architecture, and antenna patterns as used in thesimulations.

FIG. 2 illustrates a 3-beam downlink/3-beam uplink architecture.

FIG. 3 illustrates a 3-beam downlink/6-column uplink architecture.

FIG. 4 illustrates a 3-beam downlink/6-beam uplink architecture.

FIG. 5 is a plot of simulated CDMA coverage loss vs. capacity fordifferent uplink architectures.

FIG. 6 shows filter specifications suitable for a 6-column/6-beam uplinkwith masthead LNA's.

FIG. 7 illustrates comparisons between a full sector antenna, a threelow cusp beam arrangement, and a six column arrangement.

FIG. 8 illustrates an example of a suitable six column masthead antennaarrangement.

DETAILED DESCRIPTION

The problem of how to enhance the uplink capacity of a base station,without the need to use separate antenna arrays for the uplink anddownlink, has been addressed by developing an antenna array having afirst beamforming arrangement for the uplink in which preferably aplurality of (sin x/x) beams are formed, and a second beamformingarrangement for the downlink in which preferably a plurality of low cuspbeams are formed. The two beamforming arrangements use a common antennaarray. This approach is described in detail below.

A key issue is to determine whether an uplink architecture to supportthe 6-column combining (or 6-beam) options is viable, due to theincreased complexity. This has not been considered before and goesagainst accepted practice. It has been concluded, as explained below,that such an architecture can be implemented for the uplink, and that itis possible for the uplink and downlink architectures to differ.

The analysis and simulation results which follow indicate betterperformance for a 6-beam uplink than for a 6-column combining scheme,although in principle the best possible performance should be similar asit is possible for the 6-column combination to apply the same transformas the 6×6 beamformer, thereby generating the (sin x/x) beams digitally.The preferred solution in terms of uplink capacity is therefore toinclude a 6×6 uplink beamformer at the masthead, either with or withoutan active masthead, depending on the coverage requirements.

As a way of increasing the uplink sensitivity, architectures in whichall six of the antenna array columns are combined coherently appearfeasible. This does increase the total cost of the cell-site but becomesa viable option if the additional array processing also provides anincrease in capacity, such that the total cost per area for a networkdeployment is reduced. This can be achieved either by combining all 12antenna columns within a sector (i.e. six array columns from 2polarisations) using digital Maximal Ratio Combination (MRC) or minimummean squared error (MMSE) combining in the Node B cabinet, oralternatively by forming six fixed polarisation diverse beams withineach sector. In both of these approaches, there are consequently 36cables per cell-site, as opposed to 18 cables if the uplink antennaconfiguration was identical to the downlink. This raises issues relatingto the weights of feeder cables and the weights of any mastheadelectronics. For such an uplink architecture, the total weight perchannel should be minimised, such that the increased gain due to arrayprocessing is not negated by the need to use very low weight (and highloss) feeder cables.

In considering the use of array processing to enhance the uplink, it isimportant to understand the capacity and link budget implications of thedifferent beamforming and maximal ratio combining (MRC) options.Simulations have been conducted for asynchronous code divisionalmultiple access (A-CDMA) and synchronous code divisional multiple access(S-CDMA) networks, modelling the capacity available for systems witheither a 3-beam uplink, 6-column MRC, or a 6-beam uplink. Our resultsfor A-CDMA networks predict an extra 2× capacity increase for either6-column MRC or 6 sin x/x beams, relative to a system with 3 deep-cuspbeams. (These configurations therefore give 6× capacity gain relative tobaseline tri-cellular.) The antenna patterns as used in the simulations,and associated implementation architecture, are shown schematically inFIG. 1.

Similarly, it can be argued that there is an additional link budget gainavailable using 6-column MRC, or 6×6 beamformer, relative to the 3-beamarchitecture. We suggest a 6.8 dB array processing gain for 6-column MRCrelative to 3.8 dB for the 3-beam architecture (assuming that the 3beams are also MRC combined, providing additional gain for the userequipment (UE) at azimuths which fall in the deep cusps of the beampattern). There is then a 3 dB gain for the 6-column or the 6-beamarchitecture relative to the 3-beam architecture.

Then it is important to demonstrate that the capacity benefits and thelink budget benefits are available in combination, as opposed toproviding either a capacity or a link budget gain. This has beenapproached via consideration of CDMA capacity equations as an aid tointerpreting the results of the capacity simulations. These capacityequations have also been used to compare the network capacities ofdifferent options, but the aim of this is to interpret the simulationswhich use representative path loss models and beam patterns and so areultimately more accurate than the simple capacity predictions. It shouldbe noted however that the simulations do not include a representation ofa maximum UE transmit power.

The following discussion presents a more detailed review of four viablearchitecture options, these being:

3 beam, no active masthead electronics

3 beam, with masthead LNA's and filters

6 column combining, no active masthead electronics

6 column combining, with masthead LNA's and filters

These are illustrated in FIGS. 2 and 3, with FIG. 4 showing the 6 beamvariants.

This capacity and link budget analysis takes a basic CDMA capacityequation and extends it to include the additional array processingfactors. The network capacity is compared for a common ‘operating point’which corresponds to a common proportion of the system ‘pole capacity’where this ‘pole’ is reached asymptotically as the system becomesinterference limited (i.e. interference to noise ratio tends toinfinity) and the number of users in the system reaches a maximum.

The A-CDMA capacity results are compared for a common ‘noise rise’, i.e.the rise in noise plus user signal power, as measured at a singleantenna column output. In this case, the interference consists of thecombined power from each of the users within the sector or beam. Interms of a link budget for a particular user, the noise rise metricincludes the power of this ‘wanted’ user.

For an S-CDMA system, the capacity is not only dependent on the noiserise, representing the amount of power from other users, but also on thedegree to which this power is orthogonal to the wanted user (due to theuse of orthogonal CDMA codes and also to dispersion). A ‘coverage loss’metric is proposed, being a measure of the increase in power for eachuser at the receiver, required in order to overcome noise andinterference from other users. This depends on both the number of otherusers and the extent to which their power is orthogonal. For thecapacity predictions included here, capacity figures are compared on thebasis of a 3 dB coverage loss, i.e. for a network in which the receivedpower from a wanted user is 3 dB higher than it would be if it were theonly user in the network.

The capacity for an A-CDMA network is defined as follows, relative tothe signal to noise plus interference ratio required at the received fora user:

$R = {\left( \frac{E_{b}}{I_{0} + N_{0}} \right) \cdot \left( \frac{r_{b}}{B} \right)}$where:

-   -   R is the signal to noise plus interference ratio required per        user (following beam and MRC gain);    -   r_(b) is the information rate; and    -   B is the CDMA chip rate (assumed to be the receiver bandwidth).

The link budget impact can be defined by the comparing the requiredpower per user relative to thermal noise:

$\frac{P_{k}}{N} = \frac{L\; R}{b\; m}$where:

-   -   P_(k) is the received power from each user in the sector;    -   N is the thermal noise level at the receiver;    -   b is the number of beams per sector;    -   m is the number of channels per beam combined in MRC; and    -   L is the coverage loss relative to a user in noise only (i.e. no        interference from other users).

So, for the case with a 3-beam polarisation diversity uplink, m=2 andb=3. Similarly for the 6-column polarisation diversity uplink, m=12 andb=1. For the 6-beam polarisation diversity uplink, m=2 and b=6. Thismakes a simple assumption that, if a sector is divided into beams, thereis a flat-topped beam pattern with gain (relative to the sector-widepattern) equal to the number of beams. Interference from adjacentsectors or beams is assumed to be included together with the other-cellinterference.

The number of users per sector is then:

$k_{A} = {b\frac{\left\lbrack {{m\left( {L - 1} \right)} + {L\; R}} \right\rbrack}{\left\lbrack {L\;{R\left( {1 + \alpha} \right)}} \right\rbrack}}$where:

-   -   k_(A) is the number of users per A-CDMA sector; and    -   a is the relative power of other-cell interference relative to        intra-cell interference (see below).

For an S-CDMA network, the link budget impact is specified as above. Thecapacity equation assumes that there are a number of non-interferingusers within the cell that use the same outer spreading code butdifferent Walsh codes. If the number of users per sector is greater thanthe number of Walsh codes, these users will be assigned a differentouter spreading code and so will cause interference to the wanted user.There is therefore a breakpoint in the capacity equation when the numberof users per sector equals the number of available Walsh codesmultiplied by the number of beams. This number of available Walsh codesis equal to the processing gain (B/r_(b)) for data links in which asingle Walsh code is used per UE uplink.

The capacity is then given by:

$\begin{matrix}{{{For}\mspace{14mu} L} < L_{B}} & {\mspace{11mu}{k_{S} = {b\frac{\left\lbrack {{m\left( {L - 1} \right)} + {L\; R\;\beta}} \right\rbrack}{\left\lbrack {L\;{R\left( {\beta + \alpha} \right)}} \right\rbrack}}}} \\{{{For}\mspace{14mu} L} \geq L_{B}} & {\mspace{14mu}{k_{S} = {b\frac{\left\lbrack {{m\left( {L - 1} \right)} + {L\;{R\left( {\beta + s - {\beta\; s}} \right)}}} \right\rbrack}{\left\lbrack {L\;{R\left( {1 + \alpha} \right)}} \right\rbrack}}}}\end{matrix}\mspace{20mu}$

And breakpoint L_(B), corresponding to the case when k=s*b

$L_{B} = \frac{m}{\left\lbrack {m - {R\left( {{\beta\left( {s - 1} \right)} + {\alpha\; s}} \right)}} \right\rbrack}$where:

-   -   k_(s) is the number of users per S-CDMA sector;    -   β is the orthogonality factor; and    -   s is the number of Walsh codes available.

Taking the S-CDMA case with s=1, it can be verified that the S-CDMAcapacity equation reduces to become the A-CDMA case. This also occurs iforthogonality is lost due to dispersion, i.e. if β=1.

In order to represent other-cell interference, the factor α includedabove has been defined by calibrating these capacity estimates againstsimulation results for the single-sector case with MSNIR combination.The resulting other-cell interference ratio (α=0.45) has then been usedin predicting capacity values for other configurations and/or the S-CDMAcases. This parameter corresponds to a ‘geometry factor’ of 0.65. Forthe 6-beam architecture, the increased beam sidelobes has beenrepresented by a value of α=0.63.

For S-CDMA, the orthogonality factor has been assumed to be β=0.5. Thisimplies that, for users with nominally orthogonal Walsh codes, a factorof 0.5× the received power is also included as interference the wanteduser.

Capacity and link budget results are presented here for E_(b)/(N₀+I₀)=2dB. This represents a 960 kbps data link with a processing gain of 6 dBwhere B=3.84 Mcps, and provides up to 4 Walsh codes available for usewith a common outer spreading code. The variation of capacity withcoverage loss for both asynchronous and synchronous systems is shown inFIG. 5.

FIG. 5 shows that, for a nominal coverage loss of 3 dB, 6-beam S-CDMAenables the greatest number of users per sector (i.e. the greatestcapacity). The next greatest capacity is obtained using 6-beam A-CDMA,followed (in order of decreasing capacity) by 6-column S-CDMA, 6-columnA-CDMA, 3-beam S-CDMA, 3-beam A-CDMA, full sector S-CDMA and finallyfull sector A-CDMA.

The link budget and capacity benefits can be summarised for a 3 dBcoverage loss as follows:

Link A-CDMA S-CDMA Option budget capacity capacity 3-beam,   0 dB  7.3users/sector ×1  9.5 users/sector ×1.3 dual-polar (ref) (ref) 6-column,+3 dB 11.1 users/sector ×1.5 12.2 users/sector ×1.7 dual-polar 6-beam,+3 dB 13.0 users/sector ×1.8 16.0 users/sector ×2.2 dual-polar

This suggests that the 6-column dual-polar uplink provides a significantcapacity increase over a 3-beam architecture. The 6-beam approach usesan alternative combination of the array columns and, from this analysis,gives a higher capacity. Simplistically, the 6-beam scheme would provide2× capacity relative to a 3-beam scheme, but some of this additionalgain is lost due to the higher sidelobes of the sin x/x beams as opposedto the deep cusps in the 3-beam pattern. The 6-column scheme provides alower capacity gain than the 6-beam scheme as users see interferencefrom all of the users within a sector, rather than just those within thesame beam. For S-CDMA, the 6-column scheme gains less from the use oforthogonal codes, relative to the beamforming schemes, as the capacityequations above assume that the Walsh code set can be used only once persector, as opposed to once per beam.

The results above can be compared with A-CDMA simulation results. For a3 dB noise rise, these results would be as follows:

A-CDMA capacity for 3 dB noise Normalised Option rise (max SNIRcombining) capacity gain 3-beam,  6.0 users/sector ×1.0 (ref.)dual-polar 6-column, 11.7 users/sector ×1.9 dual-polar 6-beam, 12.1users/sector ×2.0 dual-polar

These results are based on full system simulation using appropriate beampatterns and representative distributions of UE's within a networklayout. In terms of capacity, the simulations can be considered to bemore accurate than the results of the analysis presented here, but theanalysis indicates that there is also a link budget gain available andthat this is provided together with the capacity benefit.

Further comparisons between a full sector antenna, a three low cusp beamarrangement, and a six column arrangement are illustrated in FIG. 7.

As described above, the capacity and link budget benefits of a 6-columnMRC or 6-beam uplink were summarised. Cost is also a key concern for thefuture system architectures. Techniques which allow the network cost tobe minimised are therefore of great interest. This may be achievedthrough reducing the cost of each Node B site, but also by providingincreased range, such that the overall number of Node B installations isreduced. Solutions providing a greater capacity or coverage per sectorare therefore likely to be more cost effective.

Masthead weight is one of the key constraints. It has been assumed herethat the total masthead weight (including feeder cables, mastheadelectronics and any additional antenna weight) cannot be increasedbeyond the weight of an existing tri-sector receive-diversity cell-site.This allows for the weight of 6 cables which are assumed to be up to 1⅝″diameter. The Andrew Corporation Heliax LDF series cable products havebeen used here as a reference, following a comparison with other cablevendors which showed these to be typical of cable insertion loss vs.weight characteristics.

Potentially, a greater weight could be allowed for a future systemarchitecture if it were to replace multiple legacy systems. The aspectis not considered in detail here as it implies multiplexing betweenoperators or frequency bands and therefore would involve additionalhardware. However, the use of shared infrastructure or multi-banddiplexers offers significant potential for reducing the overall weightof the tower installation.

Typical cell-site tower installations are rated to carry a maximum of12⅝″ diameter cables. This is consistent with the supported antennainstallation of tri-sector GSM and dual-band DCS1800/UMTS each withreceive diversity. This provides an indication of the upper bound to thetotal weight that may be permitted for a future system architecturesupporting multiplexed legacy systems.

Comparing costs for a dense urban high-base environment, assuming 30 mfeeder cables, there is a lower network cost for installations using the6-beam (or 6-column) uplink scheme. There is a potential 38% improvementin cost of Node B's per uplink capacity provided. In terms of coverage,the lowest cost per unit area is given using the 6-beam uplink combinedwith masthead LNA's. If masthead LNA's are not included, the cost perunit area is not significantly improved over the 3-beam uplink (althoughthere is still a capacity doubling) as the link budget benefits of theadditional interference and noise reduction are negated by the highermasthead cost. It should also be noted that the masthead weight for the6-beam uplink does not increase relative to the 3-beam design, andcurrent estimates actually show a useful reduction. The costs hereexclude the site and backhaul costs which would also tend to de-weightthe increase in masthead cost over a larger coverage area.

Results for dense urban low base (20 m feeder cables) and suburban pathloss model (40 m cables) are very similar. In the suburban case, the3-beam architecture including masthead amplifiers provides the best costper unit area ratio. The 6-beam uplink including masthead amplifiers hasalmost as good a cost per unit area ratio, but with the additionalbenefit of the capacity doubling

Thus, the proposed preferred beamformer design uses a 6×6 Butler matrixfollowed by combiners to pair up beam ports such that three dual polarlow cusp beams are formed for the downlink, and six (sin x/x) beams(also dual polar) are formed for the uplink. The appropriate rfcircuitry (e.g. circulators, filters etc.—as shown, for example, in FIG.4) are incorporated in a common array. Circulator devices typicallyoffer a 20 dB isolation with minimal cost or weight compared to filterstructures. This isolation assists in reducing filter requirementswithout the need for physical separation of the antenna elements.Circulators are a device which allows the downlink and uplink signals tobe discriminated (based on the signal direction of propagation), suchthat they follow different paths at the masthead (e.g. downlink througha 3×6 beamformer and uplink through the LNA). It should be noted thatcirculators provide one implementation method, but any means ofseparating the uplink and downlink signals would be applicable. Onealternative is to use filters (particularly diplexer filters) in whichthe discrimination is based on the use of different frequency bands foruplink and downlink signals. However, our proposed design usescirculators as one possible means of implementation without excessiveweight, based on a prediction of future component capabilities.

This is an optimum arrangement for the downlink in terms of efficientuse of PA's and cost per unit of capacity (as discussed in U.S. Pat. No.6,480,524). Using six (sin x/x) beams for the downlink would besub-optimal due to beam overlap. However, this does not impact theuplink similarly, and six (sin x/x) beams offer approximately twice thecapacity of three low cusp beams for the uplink.

An efficient arrangement using circulators at the masthead has beenfound which allows three beam downlink and six beam uplink (for bothpolarisations), as shown in FIG. 4. A six column arrangement is shown inFIG. 3. More cables are required, but these may be of reduced diametersuch that the total weight, wind loading and cost are maintained, andthe uplink link budget is also enhanced due to the extra combining gainprovided.

Filter specifications suitable for the 6-column/6-beam uplink withmasthead LNA's are shown in FIG. 6.

An example of a suitable six column masthead antenna arrangement isillustrated in FIG. 8. This arrangement uses +45°/−45° dual polarisationover six columns to generate 12 beams. Each X-shaped component comprisesa +45° element and a −45° element. Using dual polarisation, the problemscaused by Doppler effects and the effects of buildings, which give riseto fading or cancellation (as a result of signal recombination) ormultipath effects, can be mitigated. The use of dual polarisation allowsdiversity gain to be achieved.

Further improvement may be achieved using MMSE combining rather than theMRC described above. MMSE combining provides benefit in particular whenthe interference distribution is spatially ‘coloured’ (i.e. correlatedfrom antenna column to antenna column, or from beam to beam). If theinterference were spatially ‘white’ (i.e. uncorrelated from antennacolumn to antenna column, or from beam to beam) then the MMSE combiningsolution would be identical to the MRC combining solution. Simulationsindicate that MMSE combining typically adds some 10-25% to the uplinkcapacity.

In another alternative embodiment the antenna array may be arranged suchthat two dual polar low cusp beams are formed for the downlink, and fourdual polar (sin x/x) beams are formed for the uplink, or indeed anymultiples of uplink and downlink beams may be chosen according toapplication requirements.

While the invention has been described according to what is presentlyconsidered to be the most practical and preferred embodiments, it mustbe understood that the invention is not limited to the disclosedembodiments. Those ordinarily skilled in the art will understand thatvarious modifications and equivalent structures and functions may bemade without departing from the spirit and scope of the invention asdefined in the claims. Therefore, the invention as defined in the claimsmust be accorded the broadest possible interpretation so as to encompassall such modifications and equivalent structures and functions. Inparticular, it will be understood that the numbers of antenna elements,beams and beam patterns may vary according to application.

LIST OF ABBREVIATIONS

-   -   CDMA Code Division Multiple Access    -   A-CDMA Asynchronous Code Division Multiple Access    -   S-CDMA Synchronous Code Division Multiple Access    -   CEM Common Element Manager    -   DPCCH Dedicated Physical Control Channel    -   DPDCH Dedicated Physical Data Channel    -   LNA Low Noise Amplifier    -   MIMO Multiple Input Multiple Output    -   MMSE Minimum Mean Squared Error    -   MRC Maximal Ratio Combining    -   MSNIR Maximal Signal to Noise plus Interference Ratio    -   PA Power Amplifier    -   UE User Equipment

List of Abbreviations CDMA Code Division Multiple Access A-CDMAAsynchronous Code Division Multiple Access S-CDMA Synchronous CodeDivision Multiple Access CEM Common Element Manager DPCCH DedicatedPhysical Control Channel DPDCH Dedicated Physical Data Channel LNA LowNoise Amplifier MIMO Multiple Input Multiple Output MMSE Minimum MeanSquared Error MRC Maximal Ratio Combining MSNIR Maximal Signal to Noiseplus Interference Ratio PA Power Amplifier UE User Equipment

What is claimed is:
 1. A method, comprising: downlinking, by a userequipment of a wireless communications network, one or more signals froma transceiver, the transceiver being coupled to: a first beamformingarrangement configured to produce dual polar uplink beams; and a secondbeamforming arrangement configured to produce a plurality of dual polardownlink beams; wherein the dual polar uplink beams and the dual polardownlink beams have antenna gain that varies with direction, wherein thefirst and second beamforming arrangements are different from oneanother, wherein the dual polar uplink beams are distinguished from thedual polar downlink beams in shape, and wherein a number of dual polaruplink beams produced is greater than a number of dual polar downlinkbeams produced; processing, by the user equipment, at least one of thesignals.
 2. The method of claim 1, wherein three dual polar beams areformed for downlink and six dual polar beams are formed for uplink. 3.The method of claim 1, wherein a number of dual polar uplink beamsproduced by the first beamforming arrangement is twice a number of dualpolar downlink beams produced by the second beamforming arrangement. 4.The method of claim 1, wherein a number of dual polar uplink beamsproduced by the first beamforming arrangement is four, and wherein anumber of dual polar downlink beams produced by the second beamformingarrangement is two.
 5. The method of claim 1, wherein a number of dualpolar uplink beams produced by the first beamforming arrangement is six,and wherein a number of dual polar downlink beams produced by the secondbeamforming arrangement is three.
 6. The method of claim 1, wherein atleast one communication over the wireless communications network andcomprising the one or more signals is a multiple input multiple outputtransmission.
 7. The method of claim 1, wherein the first beamformingarrangement and the second beamforming arrangement are coupled to acommon array of antenna elements.
 8. The method of claim 1, furthercomprising uplinking at least one signal to the transceiver.
 9. Amethod, comprising: downlinking, by a user equipment of a wirelessnetwork communications system, one or more signals from an antennaarray, the antenna array comprising: a first beamforming arrangement forproducing uplink beams having a first number of uplink beams, whereinthe first beamforming arrangement is configured to produce dual polarsin x/x uplink beams; and a second beamforming arrangement for producingdownlink beams having a second number of downlink beams different fromthe first number of uplink beams; and processing, by the user equipment,at least one signal of the one or more signals.
 10. The method of claim9, wherein the first number of uplink beams is greater than the secondnumber of downlink beams.
 11. The method of claim 9, wherein the firstnumber of uplink beams is twice the second number of downlink beams. 12.The method of claim 9, wherein the first number of uplink beams is sixand the second number of downlink beams is three.
 13. The method ofclaim 9, wherein the second beamforming arrangement is configured toproduce low cusp downlink beams.
 14. The method of claim 9, wherein thesecond beamforming arrangement is configured to produce dual polar lowcusp downlink beams.
 15. The method of claim 9, wherein at least onecommunication over the wireless network communications system andcomprising the one or more signals is a multiple input multiple outputtransmission.
 16. The method of claim 9, wherein the first beamformingarrangement and the second beam forming arrangement are coupled to acommon array of antenna elements.
 17. The method of claim 9, furthercomprising uplinking one or more signals to the antenna array.